Extinction refers to the dark, unreflective areas that appear within a faceted gemstone when light escapes through the pavilion rather than returning to the observer's eye. Visible as patches of blackness or deep shadow when a stone is viewed face-up, extinction is among the most consequential optical defects a cut can produce, directly undermining brilliance, scintillation, and — in the trade — value. It arises from a failure of internal reflection: where a well-proportioned pavilion acts as a mirror system, bouncing incoming light back through the crown, an incorrectly angled or asymmetrical pavilion allows rays to exit through the base of the stone, leaving corresponding zones of the face-up view dark and lifeless.

The Optics of Extinction

To understand extinction, it is necessary to consider the principle of total internal reflection (TIR). When light travelling inside a denser medium — the gemstone — strikes a facet at an angle shallower than the critical angle for that material, it passes through rather than reflecting back. The critical angle is determined by the refractive index (RI) of the stone: a high-RI material such as demantoid garnet (RI approximately 1.88) has a relatively small critical angle and retains light more readily across a wider range of pavilion angles, while a lower-RI material such as quartz (RI approximately 1.55) demands more precise cutting to achieve the same effect. When pavilion facets are angled too shallowly or too steeply relative to the optimum for a given RI, TIR fails across those facets, and the corresponding zones in the face-up view go dark.

Extinction is therefore not a fixed defect in the rough but an outcome of cutting decisions — pavilion angle, depth percentage, symmetry, and facet layout all contribute. A stone cut to the correct pavilion angle for its refractive index will exhibit minimal extinction; the same rough cut carelessly will show broad dead areas regardless of its colour or clarity.

Common Patterns and Causes

Extinction manifests in several recognisable patterns depending on the cut style and the nature of the proportioning error.

• Bow-tie extinction: The most widely discussed form, the bow-tie is a shadow shaped like a man's bow tie that appears across the centre of elongated fancy cuts — ovals, marquises, pear shapes, and hearts. It results from the geometry of elongated outlines: the central facets of such cuts subtend angles that inevitably direct some light away from the observer. A degree of bow-tie is inherent to these shapes; the cutter's skill lies in minimising it through careful pavilion angle selection and facet layout. A pronounced, heavily dark bow-tie is a sign of poor cutting and significantly diminishes a stone's desirability. The bow-tie is assessed visually and, in some laboratory reports, noted qualitatively.
• Generalised dark zones in rounds: A standard round brilliant cut to incorrect pavilion angles — too shallow (producing a window, where the observer sees through the stone) or too steep — can show broad extinction zones across the table or around the girdle. Steep pavilions in particular tend to produce dark rings or patches rather than the transparent window associated with shallow cuts.
• Asymmetric extinction: Poor symmetry — misaligned culets, tilted tables, uneven facet placement — creates extinction that is unevenly distributed, with one side of the stone appearing darker than the other. This is especially apparent when the stone is rocked gently under a single light source.
• Step-cut extinction: Emerald cuts, Asscher cuts, and other step cuts are structurally more prone to extinction than brilliant cuts because their large, open facets offer fewer opportunities to redirect light. Well-proportioned step cuts display a characteristic hall-of-mirrors effect; poorly proportioned ones show large, static dark rectangles that do not shift with movement.

Extinction Versus Windowing

Extinction and windowing are opposite failure modes of the same optical system, and distinguishing them is important. A window occurs when the pavilion is too shallow: light passes straight through the stone, and the observer sees the surface beneath — a tabletop, a finger — rather than reflected light. The stone appears transparent and washed out in the centre. Extinction, by contrast, occurs when light exits the pavilion at angles that do not return to the eye, producing darkness rather than transparency. In practice, a single poorly cut stone may exhibit both: a central window surrounded by zones of extinction, particularly in overly flat fancy cuts. The two defects are assessed differently — windowing is most apparent over a light background, extinction over a dark one — and both are evaluated in gemmological grading as components of overall cut quality.

Factors Influencing Severity

Several variables determine how pronounced extinction will be in a given stone.

• Refractive index: As noted, higher-RI gems are more forgiving of slight angular deviations. Sphalerite (RI up to approximately 2.37) and diamond (RI 2.417) retain light across a broader range of pavilion angles than, say, fluorite (RI 1.434). A quartz oval with a mediocre pavilion angle will show a more severe bow-tie than a similarly cut zircon.
• Outline and length-to-width ratio: The more elongated a fancy cut, the more pronounced its inherent bow-tie tendency. An oval at a 1.5:1 ratio will generally show less bow-tie than one at 2.0:1, all else being equal.
• Facet count and arrangement: Brilliant-style faceting, with its multiple triangular and kite-shaped facets, distributes light return across many angles and tends to break up extinction into smaller, less visible patches. Step cuts concentrate extinction into large, visually dominant zones.
• Viewing conditions: Extinction is most apparent under diffuse, overhead lighting — the conditions that simulate how a gem looks in everyday wear. Under a single point-source light, even a poorly cut stone may appear to sparkle; the defect becomes fully evident only when the stone is assessed under the broader illumination that gemmologists and experienced buyers use for cut evaluation.

Assessment and Grading

No universally standardised grading scale for extinction exists across all laboratories, but the concept is embedded in cut-quality assessments. The Gemological Institute of America's cut-grading system for round brilliant diamonds incorporates light performance modelling that penalises stones with significant dark areas in the face-up view. For coloured stones, where no equivalent standardised cut grade applies, extinction is assessed visually by the grader and may be noted in laboratory reports — particularly for fancy cuts where bow-tie is prominent. Lotus Gemology and other specialist coloured-stone laboratories may comment on cut quality, including extinction, as part of a comprehensive report.

In practical trade evaluation, an experienced buyer will rock a stone gently under diffuse light, observing whether dark zones are static (indicating structural extinction from fixed pavilion geometry) or shift and diminish with movement (indicating normal, acceptable contrast that contributes to scintillation). Static, immovable dark areas are the hallmark of true extinction; dynamic contrast is a sign of a well-cut stone.

Commercial and Value Implications

Extinction has direct consequences for a stone's market value. In diamonds, the GIA cut grade already prices this in: an Excellent-cut round commands a premium over a Good or Poor cut, and a significant part of that premium reflects superior light return and minimal extinction. In coloured stones, where cutting standards are historically less rigorous — partly because cutters often prioritise weight retention from expensive rough over optical performance — extinction is widespread and frequently underappreciated by buyers unfamiliar with cut evaluation. A deeply saturated ruby or sapphire can mask moderate extinction through sheer colour intensity, but under careful examination the dead areas will be apparent and will reduce the stone's brilliance relative to a well-cut equivalent.

Recuts — the process of re-faceting a stone to improve its proportions — are sometimes undertaken specifically to reduce extinction, accepting a loss of weight in exchange for improved light performance and, consequently, higher per-carat value. Whether a recut is economically justified depends on the severity of the extinction, the value of the rough material, and the weight that would be sacrificed.

Further Reading

• GIA — Diamond Cut Grading (Gems & Gemology)
• GIA — How GIA Grades Diamond Cut
• International Gem Society — Windowing and Extinction in Gemstones